.. is driving me mad.

Does anyone know how licensing works? There are so many different types of licenses and so many different licensing options that I've read about that my head is about to explode!!!

Does anyone know of a site that explains how many licenses I should get and why? Licenses aren't cheap, and I don't want to buy more than required.

I have way too many questions to ask, but some of them are: Is there any difference between running a domain and a workgroup (license-wise), does the server check if I have enough licenses and if so, does it tell me (so I can buy them).

I also have questions regarding Terminal Server... but I'll figure Windows Server 2003 first.